To provide a bearing device moving an inner ring of a bearing in an axial direction by thermal displacement of seats between inner rings with a simple structure and inhibiting change of preload due to the thermal displacement.

The seat 8 between the inner rings is composed of material having larger thermal expansion coefficient than thermal expansion coefficient of a rotary shaft 5, a spacer 7 is composed of material having smaller thermal expansion coefficient than thermal expansion coefficient of the rotary shaft 5. Difference L1 of displacement between the seat 8 between the inner ring thermally displaced by heat generated at bearings 3, 4 by rotation of the rotary shaft 5 and the rotary shaft 5 near the seat between the inner ring are offset by difference L2 of displacement of the space 7 thermally displaced by the heat and the rotary shaft 5 near the spacer 7.